Hydrodynamics and mass transfer performance of rotating sieved disc contactors used for reversed micellar extraction of protein

The extraction of protein by continuous liquid-liquid extraction was investigated in a rotating disc contactor (RDC) and a rotating sieved disc contactor (RSDC) with and without stators. Hydrodynamics and mass transfer performance for reversed micellar extraction of lysozyme in RDC/RSDC I and RSDC II have been investigated. The dispersed phase holdup has increased with the increase of rotor speed. Pratt's equation was used for calculating the characteristic velocity. An inverse relation was observed between the characteristic velocity and rotor speed. The estimated overall mass transfer coefficient was increased by increasing the rotor speed. For an extraction column, the overall hydrodynamics and mass transfer performance can be judged by a volumetric utilization factor. At high rotor speeds, volumetric utilization factor for RSDCs is higher than that of RDC. The RSDC II has been successfully applied in reversed micellar extraction of protein.     

Continuous aqueous two-phase extraction of α-lactalbumin from whey in conventional rotating disc contactor

The differential partitioning of α-La to the PEG-rich phase and β-Lg to the salt-rich phase was studied in the continuous extractor, rotating disc contactor (RDC), using polyethylene glycol (PEG) 1000–trisodium citrate system. The performance of the extractor was evaluated in terms of holdup, mass transfer coefficient, extraction efficiency, and recovery by studying the operating variables such as phase velocities and rotor speed. The process conditions for the maximum dispersed phase mass transfer coefficient and recovery of α-La was also obtained and reported.     

Hydrodynamic and mass transfer parameter correlations for the rotating disc contactor

The normal, fragmented manner in which various model hydrodynamic and mass transfer parameters are measured and correlated separately, in the vain hope that accurate predictions of extraction column performance will be eventually possible, is avoided here. The ‘forward mixing’ model parameters are all determined simultaneously, in experiments with two sizes of rotating disc contactor where all required measurements, including drop size distributions and continuous phase profile compositions, are made during solute transfer between phases. Accurate predictions from the derived correlations of dispersed phase hold-up fraction, drop size distributions and extraction efficiency are the result.     

Deacidification of corn oil by solvent extraction in a perforated rotating disc column

The deacidification of corn oil by continuous liquid-liquid extraction was investigated in a rotating disc column. The solvent was ethanol containing approximately 6% water. The influence of rotor speed, oil phase flow, and column geometry upon the dispersed phase holdup and the mass transfer efficiency was studied. The dispersed phase holdup increased with the increase of rotor speed and oil phase flow. Pratt's equation was used for calculating the characteristic velocity. An inverse relation was observed between the characteristic velocity and rotor speed, which is different from data previously reported in the literature. The estimated volumetric mass transfer coefficients increased as rotor speed and oil phase flow increased. The experimental results proved that it is feasible to obtain a refined oil with an oleic acid content less than 0.3 wt% by continuous solvent extraction. They also indicated that the corresponding loss of neutral oil was less than 5 wt%. Such value for the loss of neutral oil is significantly lower than the results reported in the literature for alkali or physical refining of corn oil.     

偏心转盘塔萃取净化湿法磷酸的研究

探讨了偏心转盘塔用于蒸馏水/湿法磷酸/磷酸三丁酯（TBP）和航空煤油实验体系的萃取特性,研究了转盘雷诺数、停留时间、相比等因素对萃取和反萃取的影响。结果表明：在优化的操作条件下,偏心转盘塔具有较高的萃取效率。萃取的最佳操作条件：当相比为4、停留时间为30 min、转盘雷诺数约为2 300时,磷萃取率可达53.77%;反萃取的最佳操作条件：当相比为6、停留时间为25 min、转盘雷诺数约为6 500时,磷反萃率可达到90.66%。     

A correlation for dispersed phase axial mixing coefficients in rotating disc contactors

A correlation for the estimation of dispersed phase axial mixing coefficients in terms of all the operating and fundamental variables was established. The proposed correlations are found to be a good representation of the present data (260 data points) obtained using four liquid‐liquid systems from two different sources. Copyright © 2005 Society of Chemical Industry     

Liquid—liquid extraction column (rotating disc contactor)—model parameters from drop size distribution and solute concentration measurements

The practical application of an extraction column model which takes into account the influence of drop-size distribution (i.e. the ‘forward mixing’ model) is brought forward by the generation, from experimental data, of values of the mass transfer and axial dispersion coefficients required by the model. Values of these coefficients were generated from drop-size distribution and solute concentration profile measurements in a 22 cm diam. rotating disc contactor. The use of the Handlos-Baron drop mass transfer model is justified. The resulting continuous phase transfer coefficients were found to be dependent only on disc speed. Continuous phase axial dispersion coefficients were much higher than tracer-correlation predicted values at higher flows, and larger drop sizes. An explanation for this is presented.     

Determining axial dispersion coefficients of pilot-scale annular pulsed disc and doughnut columns

In this study, a computational fluid dynamics(CFD) method was adopted to calculate axial dispersion coefficients of annular pulsed disc and doughnut columns(APDDCs). Passive tracer was uniformly injected by pulse input at the continuous phase inlet, and its concentration governing equation was solved in liquid–liquidtwo-phase flow fields. The residence time distributions(RTDs) were obtained using the surface monitoring technique. The adopted RTD–CFD method was verified by comparing the axial dispersion coefficient between simulation and experimental results in the literature. However, in pilot-scale APDDCs, the axial dispersion coefficients predicted by the CFD–RTD method were approximately three times larger than experimental results determined by the steady-state concentration profile method. This experimental method was demonstrated to be insensitive to the variation of the axial dispersion coefficient. The CFD–RTD method was more recommended to determine the axial dispersion coefficient. It was found that the axial dispersion coefficient increased with an increase in pulsation intensity, column diameter, and plate spacing, but was little affected by the throughput.     

Hydrodynamics,axial mixing and mass transfer in open turbine rotating disc contactor (OTRDC)

An experimental study of hydrodynamics, axial mixing and mass transfer has been carried out in a newly developed liquid-liquid extraction contactor, namely the open turbine rotating disc contactor (OTRDC). It has been established that the OTRDC can be operated with larger holdups of the dispersed phase, larger interfaces and, hence, more efficient mass transfer than the conventional RDC. In correlating axial mixing data, a combined model has been applied in which both the forward mixing due to drop size distribution and the backmixing of droplets are taken into account. The RTD curves of dispersed phase predicted by the model agree well with the experimental data. Comparison of experimental mass transfer data with those predicted by the proposed axial mixing model and the theoretical single drop model shows that they are in good agreement.     

Use of axial dispersion model for determination of Sherwood number and mass transfer coefficients in a perforated rotating disc contactor

The mass transfer process in a perforated rotating disk contactor (PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.     

Axial mixing and scaleup of reciprocating plate columns

Axial mixing measurements in single phase (water) flow have been taken in open-type reciprocating plate columns of diameters 25.4 and 508 mm. In the case of the smaller column, two-phase axial mixing was measured, both in the dispersed phase (water dispersed in n-heptane) and the continuous phase (with n-heptane dispersed in water). Pulse injection of a tracer solution of ammonium chloride and methanol in water was used. Under single phase conditions, the axial dispersion coefficients were found to go through a minimum as the agitation level was increased from zero. The coefficients were nearly an order of magnitude higher in the 508 mm column than in the 25,4 mm column. In two phase flow in the 25,4 mm column, the continuous phase axial dispersion coefficients also went through a minimum as agitation was increased. The dispersed phase axial dispersion coefficients decreased monotonically as agitation was increased from zero. The results of this work and previous data are used in modelling the scale-up of reciprocating plate columns by means of Pratt's simplified technique. The existing empirical scale-up equation is consistent with an assumption that continuous phase mixing increased with column diameter but dispersed phase mixing remains unchanged.     

新型转盘萃取塔研究开发与工业应用

采用激光多普勒测速仪(LDV)和计算流体力学(CFD)软件,对转盘萃取塔(RDC)内的单相流流场进行了测量和模拟。发现塔内存在沟流和级间的旋涡流动,级间返混严重,为此发明了一种装有级间转动挡板的新型转盘萃取塔(NRDC)。NRDC与传统的RDC的区别在于安装了设计独特的转动挡板。这些转动挡板安装在2个转盘之间,固定在转动轴上,并与固定环处于同一水平面。LDV测量和CFD模拟结果发现,NRDC可有效抑制沟流和级间旋涡流动。传质实验和流体力学表明,NRDC的传质效率比RDC高20%—40%,而液泛速度大致相当。成功地将NRDC用于引进RDC的扩能改造和新塔的设计中。     

Prediction of mass transfer coefficients in an asymmetric rotating disk contactor using effective diffusivity

Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Gr?ber equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.     

Characterization of hydrodynamic parameters in rotating disc and oldshue-rushton columns. Hydrodynamic modelling,drop size,hold-up and flooding

Flooding rates, dispersed phase hold-up, hold-up profile and drop-size distribution were investigated in rotating disc and Oldshue Rushton 0.10 m diameter, 18 compartment columns with toluene-water as the liquid-liquid system. The axial dispersed phase hold-up and the mean drop size in both contactors varied significantly with column height. The hold-up profiles were correlated by semi-theoretical models.     

基于均龄理论高效计算萃取塔轴向混合分布

在验证了CFD单相流场模拟的基础上,采用均龄理论计算了中试转盘塔内的轴向混合分布,并将计算结果和理论平均停留时间以及组分输运模型计算值进行对比。结果表明:均龄理论能准确预测转盘塔内的轴向混合信息,且其计算时间只需数十秒,远小于传统组分输运模型所需的两周时间,具有低计算量的特点;同时均龄理论克服了传统组分输运模型无法模拟轴向混合空间分布的缺陷,为萃取塔内部结构优化提供了更多信息,是一种高效的模拟方法。后续均龄理论模拟结果的分析预示着转盘塔内的流动近似呈现出级内全混、级间平推的特点,符合萃取操作的需求;而相对于转盘间良好的混合作用,静环间存在明显的流动死区,造成一定的非理想性,其结构有待于进一步的优化。     

开孔转盘塔(RPDC)连续相流体轴向混合的研究

本文采用非理想脉冲示踪技术,借助于计算机数据采集系统,在无传质条件下对RPDC连续相流体的轴向混合进行了研究。用时间域最小二乘拟合法求取了轴向混合参数,分析了RPDC连续相轴向混合的机理,得到了描述连续相流体轴向混合的数学表达式。     

Prediction of mass transfer coefficients in a pulsed disc and doughnut extraction column

A study of the mass transfer performance for a pulsed disc and doughnut extraction column has been presented for a range of operating conditions. The mass transfer performance has been investigated for both directions of mass transfer. This study has examined the mass transfer coefficients which has incorporated the effects of back‐mixing in the continuous phase. The effect of operating variables including pulsation intensity and dispersed and continuous phase velocities on volumetric overall mass transfer coefficient has been investigated. The experiments showed that mixer‐settler, transition and emulsion regimes exist in the column depending on the pulse characteristics. In the present work, effective diffusivity is substituted for molecular diffusivity in the Gröber equation for estimation of overall mass transfer coefficients. The enhancement factor is determined experimentally and there from a single empirical correlation is derived for prediction of enhancement factor in terms of Reynolds number, holdup and Eötvös number for all operating regimes and each mass transfer direction. The experimental results are in very good agreement with the values calculated by the proposed equation. © 2011 Canadian Society for Chemical Engineering     

Suggestion of a New Correlation for the Height of Shallow Dispersion Bed Formed in a Rotating Disc Contactor

A rotating disc contactor (RDC) was designed and constructed. The obtained experimental results for the heights of shallow dispersion beds formed in the separation zone of the extraction column, suggested a new correlation. It was found that any increase in dispersed phase flow rate or rotor speed caused an increase in the dispersion height. Also, the results revealed the profound effect of the continuous phase viscosity on the height of the bed. Within the ranges of experimental results, the proposed correlation was in good agreement with the data of shallow beds compared to previous proposed relations.     

转盘塔内甲基异丁基酮萃取湿法磷酸实验研究

溶剂萃取法是一种经济有效的湿法磷酸净化方法。在转盘塔中,以甲基异丁基酮（MIBK）为萃取剂,开展了净化湿法磷酸的实验研究。考察了搅拌转速、相比对磷酸萃取率、杂质离子选择性、洗涤效果和反萃效果的影响。研究结果表明：萃取过程适宜的相比（溶剂与磷酸的体积比）为4,搅拌转速为200~400 r/min,在此条件下磷酸萃取率为85%;洗涤过程的搅拌转速不应大于100 r/min,适宜的洗涤酸用量为溶剂相体积的10%~15%,在此条件下铁离子（Ⅲ）和镁离子脱除率均在90%以上、铝离子脱除率大于70%、硫酸根脱除率为50%~60%;反萃过程搅拌转速不应大于200 r/min,适宜的反萃水用量为溶剂相体积的9%~15%。MIBK对阳离子的脱除效果较好,但是对阴离子的脱除效果不佳。经过萃取、洗涤和反萃3个过程,磷酸收率为57.8%~70.3%,磷酸中铁离子（Ⅲ）含量可以达到工业级磷酸标准,但是硫酸根的含量无法达标,需要结合其他方法进一步脱除。     

The Interaction of solute transfer,contaminants and dro break-up in rotating disc contactors: Part II. The coupling of the mass transfer and breakage processes via interfacial tension

In order to investigate the influence of solute transfer and of surface active agents on the drop breakage process in liquih liquid extraction columns, their effect on the interfacial tension has to be studied in detail. The difficulty encountered is that the interfacial tension during solute transfer continuously changes and that no simple apparatus is commercially available which can measure these varying interfacial tension values. An attempt has been made here to theoretically predict them. The equations developed to predict the interfacial tension variation can be combined with a model for the breakage process and hence drop size distributions can be calculated from stage to stage. Applying a new combined film mass transfer coefficient model which takes into account the effect of contaminants, single drop extraction performance has been calculated for simplified conditions of constant bulk concentration in the continuous phase. Calculated efficiencies have been compared with experimental data and a good simulation of contaminant effects and dependency on drop size has been found. The calculations were restricted to low dispersed phase hold-up values, so that coalescence effects could be ignored. This work provides the required support for a procedure to be applied to counter-current flow extraction columns.